My guess for the increases sales would be the Alabama plant is now fully online. One thing to keep in mind is that they are not making twice as many now as compared to last year. This is because Ontairo is now making the Pilot to take away from some of their Ody production. However, Alabama is going to double their capacity. That should provide another spike in sales once it happens.
Good point about increased production. The sales numbers going up shouldn't surprise anyone. If Honda can sell all they make and also control how many they make, they can control the market. Sales can(theoretically)increase by as much as production increases for as long as production increases(barring major quality issues and other variables some of which may be beyond Honda's control). As long as people are buying other minivans, there is a market out there for the Odyssey to tap into. Limited production is part of Honda's strategy and the reason why Ody owners enjoy such high resale value.